Process for producing gasoline of increased octane and hydrogen-containing co-produced stream

ABSTRACT

The present invention is directed to a process for producing an increased yield of gasoline of increased octane rating by the integration of a membrane separation processing step into the gasoline production process. The integrated process also increases hydrogen production from the reformer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the production of gasoline, to the increase of the octane rating of the gasoline so produced and to the production of hydrogen.

2. Description of the Related Art

The use of membrane separation processes to divide feed streams into permeate streams and retentate streams of different chemical composition is well known in the art.

The removal of aromatic hydrocarbons from feed streams containing mixtures of aromatic hydrocarbons and non-aromatic hydrocarbons using membranes is a desirable process which has been described in the patent literature.

U.S. Pat. No. 2,947,687 teaches the separation of hydrocarbons by type through a non-porous membrane using a membrane solvent to enhance the permeation rate. Membrane solvents include substituted hydrocarbons which are soluble in and have solvent power for the membrane. The hydrocarbon solvent is an organic compound containing one or more atoms of halogen, oxygen, sulfur or nitrogen. Thus, materials such as carbontetrachloride, alcohols, ketones, esters, ethers, carboxylic acids, mercaptans, sulfides (e.g., diethylsulfide, etc.), nitropropane, nitrobenzene, acetonitrile, formamide, ethylene diamine, etc. may be employed in an amount ranging from 1 to 100% based on total solvent to hydrocarbon feed. The process may be operated at a pressure differential between the feed and permeate zone with a permeate being removed by vacuum. Alternately, the permeate can be removed by a sweep stream such as steam, air, butane, etc.

The membrane is non-porous and includes natural or synthetic rubber, vinyl polymers, cellulose esters, cellulose ethers.

The process can use any hydrocarbon source as feed and the separation achieved is in the order: saturated hydrocarbons, <unsaturated hydrocarbons, <aromatics. Saturated hydrocarbons of approximately the same boiling range permeate in the order of increasing selectivity: branched chain, <cyclic-chain, <straight chain configuration; i.e., straight chain paraffins more readily permeate through the membrane.

U.S. Pat. No. 3,140,256 teaches a membrane separation process employing a membrane comprised of a cellulose derivative (e.g., cellulose ester or ether) modified by reaction with aldehydes, organic diisocyanate, organic monoisocyanate, organo-phosphorus chlorides and organo-sulfur chlorides. Hydrocarbon feeds can be separated into these components by type using the membrane; e.g., aromatics can be separated from unsaturated hydrocarbon (olefins or diolefins) and/or from paraffins, or branched chain aliphatic hydrocarbons can be separated from other aliphatic hydrocarbons which have a different number of branched chains. Aromatic hydrocarbons permeate more rapidly than do the saturated (i.e., paraffinic) hydrocarbons. In an example, methyl cyclohexane permeated through the membrane more selectively than did isooctane.

U.S. Pat. No. 3,370,102 teaches the membrane separation of aromatics from saturates in a wide variety of feed mixtures including various petroleum fractions, naphthas, oils, and other hydrocarbon mixtures. Expressly recited in '102 is the separation of aromatics from kerosene. The process produces a permeate stream and a retentate stream and employs a sweep liquid to remove the permeate from the face of the membrane to thereby maintain the concentration gradient driving force. U.S. Pat. No. 2,958,656 teaches the separation of hydrocarbons by type; i.e., aromatics, unsaturated, saturated by permeating a portion of the mixture through a non-porous cellulose ether membrane and removing permeate from the permeate side of the membrane using a sweep gas or liquid. Feeds include hydrocarbon mixtures (including virgin naphtha, naphtha from thermal or catalytic cracking, etc.) U.S. Pat. No. 2,930,754 teaches a method for separating hydrocarbons by type; i.e., aromatics and/or olefins from gasoline boiling range mixtures by the selective permeation of the aromatics through certain cellulose ester non-porous membranes. The permeated hydrocarbons are continuously removed from the permeate zone using a sweep gas or liquid. U.S. Pat. No. 4,115,465 teaches the use of polyurethane membranes to selectively separate aromatics from saturates via pervaporation.

Polyurea/urethane membranes and their use for the separation of aromatics from non-aromatics are the subject of U.S. Pat. No. 4,914,064. In that case the polyurea/urethane membrane is made from a polyurea/urethane polymer characterized by possessing a urea index of at least about 20% but less than 100%, an aromatic carbon content of at least about 15 mole percent, a functional group density of at least about 10 per 1000 grams of polymer, and a C═O/NH ratio of less than about 8.0. The polyurea/urethane multi-block copolymer is produced by reacting dihydroxy or polyhydroxy compounds, such as polyethers or polyesters having molecular weights in the range of about 500 to 5,000 with aliphatic, alkylaromatic or aromatic diisocyanates to produce a prepolymer which is then chain extended using diamines, polyamines or amino alcohols. The membranes are used to separate aromatics from non-aromatics under perstraction or pervaporation conditions.

Thin film compositions can be prepared either from suspension deposition as taught in U.S. Pat. No. 4,861,628 or from solution deposition as taught in U.S. Pat. No. 4,837,054.

The use of polyurethane imide membranes for aromatics from non-aromatics separations is disclosed in U.S. Pat. No. 4,929,358. The polyurethane-imide membrane is made from a polyurethane-imide copolymer produced by end capping a polyol such as a dihydroxy or polyhydroxy compound (e.g., polyether or polyester) with a di- or polyisocyanate to produce a prepolymer which is then chain extended by reaction of said prepolymer with a di- or polyanhydride with a di- or polycarboxylic acid to produce a polyurethane/imide. The aromatic/non-aromatic separation using said membrane is preferably conducted under perstraction or pervaporation conditions.

A polyester imide copolymer membrane and its use for the separation of aromatics from non-aromatics is the subject of U.S. Pat. No. 4,946,594. In that case the polyester imide is prepared by reacting polyester diol or polyol with a dianhydride to produce a prepolymer which is then chain extended preferably with a diisocyanate to produce the polyeseter imide.

U.S. Pat. No. 4,929,357 is directed to non-porous isocyanate cross-linked polyurethane membranes. The membrane can be in the form of a symmetric dense film membrane. Alternatively, a thin, dense layer of isocyanurate cross-linked polyurethane can be deposited on a porous backing layer to produce a thin film composite membrane. The isocyanurate cross-linked polyurethane membrane can be used to separate aromatic hydrocarbons from feed streams containing mixtures of aromatic hydrocarbons and non-aromatic hydrocarbons, the separation process being conducted under reverse osmosis, dialysis, perstraction or pervaporation conditions, preferably under perstraction conditions.

U.S. Pat. No. 4,962,271 teaches the selective separation of multi-ring aromatic hydrocarbons from distillates by perstraction. The multi-ring aromatics are characterized by having less than 75 mole % aromatic carbon content. Perstractive separation is through any selective membrane, preferably the aforesaid polyurea/urethane, polyurethane imides or polyurethane isocyanurates.

U.S. Pat. No. 4,990,275 relates to a copolymer composition comprising a hard segment of a polyimide and a soft segment of an oligomeric aliphatic polyester. Membranes made from the copolymer are useful for aromatic/saturates separations. The polyimide is derived from a dianhydride having between 8 and 20 carbons and a diamine having between 2 and 30 carbons while the oligomeric aliphatic polyester is a polyadipate, polysuccinate, polymalonate, polyoxalate or polyglutarate.

U.S. Pat. No. 4,962,270 teaches the improved separation of feed streams containing multiple components affected by means of a multi-membrane staged pervaporation process wherein each membrane stage in series is run at progressively higher temperature, stronger vacuum or both than the preceding stage. This process is especially useful for separating components from wide boiling range mixtures. The separation of a multi-component feed mixture of aromatic hydrocarbons and non-aromatic hydrocarbons is specifically mentioned.

U.S. Pat. No. 5,095,171 teaches that the separation of aromatic hydrocarbons from mixtures of aromatic and non-aromatic hydrocarbon feeds under pervaporation conditions is improved by the control of the amount of oxygen present in the feed. The amount of oxygen in the feed, such as heavy cat naphtha or other cracked feed, should be less than 30 wppm, preferably less than 10 wppm. The oxygen level in the feed can be controlled by the addition of small amounts of oxygen scavenger into the feed. Hindered phenols are representative of useful oxygen scavengers. Hydrocarbon feeds which can be subjected to the control of oxygen content include any cracked feed including by way of example light cat naphtha, intermediate cat naphtha, heavy cat naphtha, jet fuel, diesel fuel, coker gas oil, in general any cracked stock boiling in the 65° to 1050° F. range.

U.S. Pat. No. 5,098,570 is directed to a multi-block polymeric material comprising an urea prepolymer chain extended with a second compatible prepolymer selected from the group of prepolymers comprising (a) an (A) dianhydride or its corresponding tetraacid or diacid-diester combined with a monomer selected from (B) epoxy, diisocyanate, polyester, and diamine in an A/B mole ratio ranging from about 2.0 to 1.05, preferably about 2.0 to 1.1, and (b) an (A) diamine combined with a monomer selected from (B) epoxy and dianhydride or its corresponding tetraacid or diacid-diester in an A/B mole ratio ranging from about 2.0 to 1.05, preferably about 2.0 to 1.1, and mixtures thereof. It is also directed to membranes of the above-recited multi-block polymeric material, especially membranes comprising them, dense films of said multi-block polymeric material deposited on a microporous support layer producing a thin film composite membrane. The membranes of the multi-block polymeric material, especially the thin film composite membranes, are useful for separating aromatic hydrocarbons from mixtures of same with non-aromatic hydrocarbons under perstraction or pervaporation conditions.

U.S. Pat. No. 5,130,017 is directed to a multi-block polymeric material comprising a first amide acid prepolymer, made by combining (A) a diamine with (B) a dianhydride or its corresponding tetraacid or diacid-diester in an A/B mole ratio ranging from about 2.0 to 1.05, preferably about 2.0 to 1.1, chain extended with a second, different, compatible prepolymer selected from the group of prepolymers comprising (A) a dianhydride or its corresponding tetraacid or diacid-diester combined with a monomer selected from (B) epoxy, diisocyanate and polyester in an A/B mole ratio ranging from about 2.0 to 1.05, preferably about 2.0 to 1.1.

It is also directed to membranes of the above-recited multi-block polymeric materials, especially membranes comprising thin, dense films of said multi-block polymeric material deposited on a microporous support layer producing a thin film composite membrane.

The membranes of the multi-block polymeric material, especially the thin film composite membranes, are useful for separating aromatic hydrocarbons from mixtures of same with non-aromatic hydrocarbons under perstraction or pervaporation conditions. Suitable feed streams for aromatics from saturates separation are heavy cat naphtha, intermediate cat naphtha (200-320° F.), light aromatics content streams boiling in the C₅-300° F. range, light catalytic cycle oil boiling in the 400-650° F. range, reformate streams as well as streams in chemical plants which contain recoverable quantities of benzene, toluene, xylene (BTX) or other aromatics in combination with saturates.

U.S. Pat. No. 5,221,481 is directed to a multi-block polymeric material comprising an ester prepolymer chain extended with a second, different, compatible prepolymer selected from the group of prepolymers comprising (a) an (A) dianhydride or its corresponding tetraacid or diacid-diester combined with a monomer selected from (B) epoxy, diisocyanate, polyester, and diamine in an A/B mole ratio ranging from about 2.0 to 1.05, preferably about 2.0 to 1.1; and (b) an (A) diamine combined with a monomer selected from (B) epoxy, diisocyanate, and dianhydride or its corresponding tetraacid or diacid-diester in an A/B mole ratio ranging from about 2.0 to 1.05, preferably about 2.0 to 1.1, and mixtures thereof. It is also directed to membranes of the above-recited multi-block polymeric materials, especially membranes comprising thin, dense films of said multi-block polymeric material deposited on a microporous support layer producing a thin film composite membrane. The membranes of the multi-block polymeric material, especially the thin film composite membranes, are useful for separating aromatic hydrocarbons from mixtures of same with non-aromatic hydrocarbons under perstraction or pervaporation conditions.

U.S. Pat. No. 5,290,452 is directed to a polyester/amide membrane, its preparation and its use for organic liquid separation. The polyester/amide membrane is made by reacting a dianhydride with a polyester diol in a 2:1 to 1.05:1 mole ratio to end cap the diol to produce a prepolymer which is reacted with excess thionyl chloride to convert all of the unreacted anhydride and all carboxylic acid groups to acid chloride groups. The resulting acid chloride derivative is dissolved in organic solvent and interfacially reacted with a diamine dissolved in an aqueous solvent. The excess solutions are removed and the resulting thin film membrane is dried. The membranes are useful for organic liquid separations, especially the separation of aromatic hydrocarbons from mixtures of same with non-aromatic hydrocarbons, preferably under perstraction or pervaporation conditions.

U.S. Pat. No. 5,416,259 teaches that the pervaporative treatment of hydrocarbon feeds which have been exposed to air or oxygen and which contain mixtures of aromatic and non-aromatic hydrocarbons to selectively separate the feed into an aromatics-rich stream and a non-aromatics-rich stream is improved by the step of pretreating the hydrocarbon feed over an adsorbent such as attapulgite clay.

U.S. Pat. No. 5,635,055 teaches that the yield and quality of products secured from cracking units is increased by the process of subjecting the product stream secured from such cracking unit to a selective aromatics removal process and recycling the recovered aromatics lean (saturates-rich) stream to the cracking unit whereby such saturates-rich stream is subjected to increased conversion to higher value desired products.

U.S. Pat. No. 5,643,422 is directed to a process whereby distillate or hydrotreated distillate effluent is separated into an aromatics-rich permeate and an aromatics-lean retentate by use of a permselective membrane with the aromatics-rich permeate being sent to a hydrotreater, thereby increasing the quantity of reduced aromatics content product. The aromatics-lean retentate can be sent downstream and blended into the jet fuel, heating oil or diesel pool.

DESCRIPTION OF THE FIGURES

FIG. 1 presents a schematic of an integrated process for the production of hydrogen and high octane gasoline or gasoline blend stock at enhanced efficiency.

DESCRIPTION OF THE INVENTION

The present invention is directed to a process for increasing the aromatic content of blend stocks used for the production of motor gasoline, thereby increasing the octane rating of the resultant fuels into which such blend stock is mixed and increasing hydrogen production without increasing reformer through-put.

In the production of hydrogen and gasoline of increased octane rating, a feed stream containing a mixture of aromatic hydrocarbons and non-aromatic hydrocarbons such as a virgin naphtha stream or a thermal cracked or catalytically cracked naphtha stream or other streams boiling in the distillate to gasoline boiling range containing aromatic and non-aromatic hydrocarbons, preferably naphtha (virgin naphtha, thermal or catalytically cracked naphtha or mixtures thereof), can be sent to a membrane separation unit employing any of the aromatics/non-aromatics/saturates separation membranes known to those skilled in the art, preferably polyester imide membrane disclosed in U.S. Pat. No. 4,946,594. While any of the membranes of the art capable of separating aromatic hydrocarbons from mixtures of aromatic hydrocarbons and non-aromatic/saturate hydrocarbons can be used in the present invention, certain membranes are preferred. A particularly preferred membrane is described in U.S. Published Application 2008/0035572, published Feb. 14, 2008 directed to a polymeric membrane composition, comprising a dianhydride, a diamine, a cross-linking agent and a difunctional dihydroxy polymer selected from:

a) dihydroxy end-functionalized ethylene propylene copolymers with an ethylene content from about 25 wt % to about 80 wt %;

b) dihydroxy end-functionalized ethylene propylene diene terpolymers with an ethylene content from about 25 wt % to about 80 wt %;

c) dihydroxy end-functionalized polyisoprenes; dihydroxy end-functionalized polybutadienes; dihydroxy end-functionalized polyisobutylenes;

d) dihydroxy end-functionalized acrylate homopolymers, copolymers and terpolymers; dihydroxy end-functionalized methacrylate homopolymers, copolymers and terpolymers; and mixtures thereof;

wherein the mixtures of acrylate and methacrylate monomers range from C₁ to C₁₈;

e) dihydroxy end-functionalized condensation homopolymers, copolymers, terpolymers and higher order compositions of structurally different monomers, including alcohol-terminated end-functionalized esters and dihydroxy end-functionalized multimonomer polyesters; and mixtures thereof;

wherein the polyalkyladipate structures range from C₁ to C₁₈;

f) dihydroxy end-functionalized perfluoroelastomers;

g) dihydroxy end-functionalized urethane homopolymers, copolymers, terpolymers, and higher order compositions of structurally different monomers;

h) dihydroxy end-functionalized carbonate homopolymers, copolymers, terpolymers, and higher order compositions of structurally different monomers;

i) dihydroxy end-functionalized ethylene alpha-olefin copolymers, dihydroxy end-functionalized ethylene propylene alpha-olefin terpolymers;

wherein the alpha-olefins are linear or branched and range from C₃ to C₁₈;

j) dihydroxy end-functionalized styrene homopolymers, copolymers, terpolymers, and higher order compositions of structurally different monomers;

k) dihydroxy end-functionalized silicone homopolymers, copolymers, terpolymers, and higher order compositions of structurally different monomers;

l) dihydroxy end-functionalized styrene butadiene copolymers, dihydroxy end-functionalized styrene isoprene copolymers; and

m) dihydroxy end-functionalized styrene butadiene block copolymers; and dihydroxy end-functionalized styrene isoprene block copolymers; wherein the polymeric membrane is compared of a hard segment and soft segment, wherein the soft segment preferably has a glass transition temperature, Tg, less than 77° F. (25° C.), more preferably less than 32° F. (0° C.), the glass transition temperature of the hard segment, preferably, is greater than 212° F. (100° C.), and the Absorbance Infra-red Spectrum of the membrane has an Aliphatic C—H Area to Aromatic C—H Area ratio of at least 10, the cross-linking agent is selected from diepoxycyclooctane, diepoxyoctane, 1,3-butadiene diepoxide, glycerol diglycidyl ether, bisphenol A diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, bisphenol F diglycidyl ether, neopentyl glycol diglycidyl ether, poly(propylene glycol) diglycidyl ether, and mixtures there, and the final polymer solution, including the cross-linking agent, is cured at a temperature from about 212° F. to about 480° F. (100° C. to about 250° C.) to form the final polymeric membrane composition.

The membrane can be made as such or can be cast on a supported material comprised of a material selected from polytetrafluoroethylene, aromatic polyamide fiber, porous metal, sintered metal, porous ceramic, polyester, nylon, activated carbon fiber, latex, silicone, polyvinylfluoride, polyvinylidenefluoride, polyurethane, polypropylene, polyethylene, polycarbonate, polysulfone, polyphenylene oxide, metal foam, polymer foam, silica, porous glass, mesh screen, and combinations thereof.

A preferred embodiment of US 2008/0035572 is described in Published Application U.S. 2008/0035571, published Feb. 14, 2008 in which it is taught that the permselective polymeric membrane film sheet of U.S. 2008/0035572 can be cross-linked to another layer of the same or different permselective polymer membrane film. The multiple membrane film sheets can comprise two to ten or more layers and can differ either compositionally (provided they are still selected from the previously recited list) and/or by concentration of the polymers used to produce the different film sheets. The multiple sheets are arranged in at least two adjacent membrane layers which are then chemically cross-linked between the contacting faces of the adjacent permselective polymer membrane layer, thereby forming an integrally layered multi-layer membrane by curing. The adjacent layer can be cross-linked by first forming a first membrane layer drying said first membrane layer to “thick” consistency (dried but not cured, drying it between about 122° F. to 257° F. (50° C. to 125° C.) being typically sufficient), depositing on said first dried but uncured membrane layer a second polymer layer to form an uncured layer membrane and curing the uncured layer membrane at a temperature of from about 212° F. to 482° F. (100° C. to 250° C.) to form the integrally-layered permselective polymeric membrane; in this instance, a two-layer membrane. A membrane of more than two layers can be made by, rather than curing the two-layer system, the two layers are dried (but not cured) and a third layer is deposited. If a three-layer system is desired, following deposition of the third layer the three-layer uncured membrane is cured. If, rather, additional layers are desired, each subsequent layer is deposited on the preceding dried but uncured multi-layer membrane, until the final desired number of layers is deposited. Once the desired number of layers is reached, the uncured multi-layer membrane is cured as previously described.

In the practice of the present invention, because of the possibility that the naphtha feed stream to the membrane might contain measurable quantities of free and/or soluble water and/or free and/or dissolved O₂, it is preferred that use be made of the membrane taught in U.S. 2008/0035574 (published Feb. 14, 2008). The preferred membrane comprises at least one permselective polymer membrane element and a hydrophobic and/or vapor barrier film layer, the hydrophobic and/or vapor barrier film layer being oriented on the feed stream side of the permselective polymer membrane element, the hydrophobic and/or vapor barrier being substantially impermeable to water and/or O₂. By “substantially impermeable” is meant that the permeate contains less than 25%, preferably less than 10%, more preferably less than 5% by volume of free and/or soluble water and/or free and/or dissolved oxygen as compared to the volume of free and/or soluble water and/or free and/or dissolved oxygen present in the original feed. The permselective polymer membrane element is preferably comprised of a dianhydride, a diamine, a cross-linking agent, and a difunctional dihydroxy polymer selected from:

a) dihydroxy end-functionalized condensation homopolymers, copolymers, terpolymers and higher order compositions of structurally different monomers, including alcohol-terminated end-functionalized esters and dihydroxy end-functionalized multimonomer polyesters; and mixtures thereof;

wherein the polyalkyladipate structures range from C₁ to C₁₈; and

b) dihydroxy end-functionalized urethane homopolymers, copolymers, terpolymers, and higher order compositions of structurally different monomers;

while the hydrophobic and/or vapor barrier is a film comprised of a compound selected from polytetrafluoroethylene, polyvinylfluoride, polyvinylidenefluride, polypropylene, polyethylene, polycarbonate, polysulfone, silicone, or a film membrane layer comprised of a dianhydride, a diamine, a cross-linking agent, and a difunctional dihydroxy polymer selected from:

a) dihydroxy end-functionalized ethylene propylene copolymers with an ethylene content from about 25 wt % to about 80 wt %;

b) dihydroxy end-functionalized ethylene propylene copolymers with an ethylene content from about 25 wt % to about 80 wt %;

c) dihydroxy end-functionalized acrylate homopolymers, copolymers and terpolymers; dihydroxy end-functionalized methacrylate homopolymers, copolymers and terpolymers; and mixtures thereof,

wherein the mixtures of acrylate and methacrylate monomers range from C₁ to C₁₈;

d) dihydroxy end-functionalized perfluoroelastomers;

e) dihydroxy end-functionalized carbonate homopolymers, copolymers, terpolymers, and higher order compositions of structurally different monomers;

f) dihydroxy end-functionalized ethylene alpha-olefin copolymers; dihydroxy end-functionalized propylene alpha-olefin copolymers; and dihydroxy end-functionalized ethylene propylene alpha-olefin terpolymers;

wherein the alpha-olefins are linear or branched and range from C₃ to C₁₈;

g) dihydroxy end-functionalized styrene homopolymers, copolymers, terpolymers, and higher order compositions of structurally different monomers; and

h) dihydroxy end-functionalized silicone homopolymers, copolymers, terpolymers, and higher order compositions of structurally different monomers.

The hydrophobic and/or vapor barrier film is as previously stated, on the feed side of the permselective polymer membrane. The barrier film can be employed as a separate sheet situated on the feed side of the permselective polymer membrane or can be directly coated onto the permselective polymer membrane as an integral layer by being sprayed on or vacuum-induced onto the permselective polymer membrane layer, or by any other known coating procedure.

Another membrane system preferably used in the present invention is described in Published U.S. Application 2008/0035566, published Feb. 14, 2008 which teaches a multi-layer membrane system comprised of at least two permselective polymer membrane layers and at least two polymer film layers wherein at least one permselective polymeric membrane layer is comprised of a dianhydride, a diamine, a cross-linking agent and a difunctional dihydroxy polymer wherein the difunctional dihydroxy polymer and the cross-linking agents are selected from the group recited in U.S. 2008/0035572. In U.S. 2008/0035566 the permselective membrane layer is formed on a support material, then has a polymer film layer of the type recited in Published U.S. Application 2008/0035574 deposited on the feed side face of the permselective membrane. In a preferred embodiment of U.S. 2008/0035574, a support material is coated both front and back with two or more integral layers of permselective polymeric membrane material, the multiple integral layers being deposited and cured as taught in U.S. 2008/0035571. This cured dual side deposited membrane element can be coated, front and back, with the polymer film layers. Alternatively, two or more of the cured dual side deposited membrane element can be formed into a stack, then have a film layer placed or deposited on the front and back faces of the stack. Such a stack element can be engineered, depending on the number of cured dual side deposited membrane elements employed, to exhibit selectively for particular different carbon number aromatics in the permeate; e.g., lower carbon number aromatics can be excluded from the permeate while higher carbon number aromatics selectively permeate through the membrane element and resulting in a higher concentration/distribution of the higher carbon number aromatics in the permeate as compared to the concentration/distribution of such aromatics in the feed stream, based on the total concentration of aromatics.

Separation in the membrane separation unit can be conducted under either perstraction or pervaporation conditions. Perstraction involves the selective dissolution of particular components contained in a mixture into the membrane, the diffusion of those components through the membrane and the removal of the diffused components from the downstream side of the membrane by use of a liquid sweep stream. In the perstractive separation of aromatics from saturates in petroleum or chemical streams (particularly heavy cat naphtha streams) the aromatic molecules present in the feed stream dissolve into the membrane film due to similarities between the membrane solubility parameter and the solubility parameter of the aromatic species in the feed. The aromatics then permeate (diffuse) through the membrane and are swept away by a sweep liquid which is low in aromatics content. This keeps the concentration of aromatics at the permeate side of the membrane film low and maintains the concentration gradient which is responsible for the permeation of the aromatics through the membrane.

The sweep liquid is low in aromatics content so as not to itself decrease the concentration gradient. The sweep liquid is preferably a saturated hydrocarbon liquid with a boiling point much lower or much higher than that of the permeated aromatics. This is to facilitate separation, as by simple distillation. Suitable sweep liquids, therefore, would include, for example, low boiling C₃ to C₆ saturated hydrocarbons and high boiling lube base stocks (C₁₅ to C₂₀). In the present invention it is preferred that the sweep liquid is itself a fraction suitable for use as gasoline or gasoline blend fraction; e.g., a high octane alkane-rich/aromatics-lean stream can be used as the sweep liquid, thus avoiding the necessity of practicing a further separation/aromatics recovery step.

The perstraction process is run at any convenient temperature, preferably as low as possible.

The choice of pressure is not critical since the perstraction process is not dependent on pressure, but on the ability of the aromatic components in the feed to dissolve into and migrate through the membrane under a concentration driving force. Consequently, any convenient pressure may be employed, the lower the better to avoid undesirable compaction, if the membrane is supported on a porous backing, or rupture of the membrane, if it is not.

Pervaporation, by comparison, is run at generally higher temperatures than perstraction and relies on vacuum on the permeate side to evaporate the permeate from the surface of he membrane and maintain the concentration gradient driving force which drives the separation process. As in perstraction, the aromatic molecules present in the feed dissolve into the membrane film, migrate through said film and re-emerge on the permeate side under the influence of a concentration gradient. Pervaporation separation of aromatics from saturates can be performed at a temperature of about 25° C. for the separation of benzene from hexane but for separation of heavier aromatic/saturate mixtures, such as heavy cat naphtha, higher temperatures of at least 80° C. and higher, preferably at least 100° C. and higher, more preferably 120° C. and higher should be used. The maximum upper temperature limit is that temperature at which the membrane is physically damaged or delaminates. Vacuum on the order of 1 to 50 mm Hg is pulled on the permeate side. The vacuum stream containing the permeate is cooled to condense out the highly aromatic permeate. Condensation temperature should be below the dew point of the permeate at a given vacuum level.

The membrane itself may be in any convenient form utilizing any convenient module design. Thus, sheets of membrane material may be used in spiral wound or plate and frame permeation cell modules. Tubes and hollow fibers of membranes may be used in bundled configurations with either the feed or the sweep liquid (or vacuum) in the interior space of the tube or fiber, the complimentary environment obviously being maintained on the other side.

In the membrane separation unit the feed is separated into an aromatics-rich/saturates-lean permeate which is a gasoline blend stock stream of increased octane rating due to the increased aromatics hydrocarbon content. The retentate stream being of reduced aromatics content/increased non-aromatics-saturates content can be employed in an integrated process as the feed stream to a reformer wherein the retentate stream feed stream is converted to high octane reformer product and a gaseous stream of co-produced hydrogen. The amount of hydrogen produced in the reformer using this retentate stream as the feed stream is greater than when using conventional reformer feed streams, without increasing reformer through-put. The reformer unit can be either a continuous catalytic reformer (CCR) or semi-regenerated reformer, both of which are well known in the refining industry. (Catalytic reforming operating in continuous catalytic regeneration mode or semi-regeneration mode upgrades low-octane naphtha (gasoline boiling hydrocarbons) into high-octane gasoline while producing hydrogen by dehydrogenation of naphthenes to aromatics. Besides producing high-octane gasoline, the catalytic reforming also provides the majority of hydrogen consumed in the refinery.)

The retentate stream sent to the reformer can be employed as such or augmented with/used in combination with the saturates-rich/aromatics-lean refinery feed stream(s) typically used as feed to reformer units. The retentate can be as 100% reformer feed or a fraction of reformer feed. The purpose is to increase hydrogen production expressed as scf/b assuming the reformer feed rate is unchanged. The reformer feed can be a mixture of straight-run naphtha, coker naphtha, FCC naphtha, and naphtha produced from various hydroprocessing units, such as resid upgrading units, FCC feed pretreating units, hydrocrackers, and/or diesel desulfurizations units. Other similar streams having a boiling range of from about 65 to about 450° F. could also be suitable. The reformer feed components should be low in sulfur and nitrogen, generally less than 1.0 ppmw. Any reformer feed components with a high concentration of sulfur and nitrogen should be treated in a naphtha pretreater to remove the residual sulfur and nitrogen down to less than 1 ppmw.

In another embodiment, in addition to or in place of such typical reformer feeds, the retentate stream can be combined with a stream produced as the retentate stream from a different membrane separation unit which operates on an aromatics/non-aromatics containing feed stream which has been subjected to a selective hydrotreatment or an FCC naphtha desulfurization step prior to the membrane separation step. The permeate from said different membrane separation unit is itself an aromatics-rich stream of increased octane which can be used as such as gasoline blending stock.

In another embodiment, a feed stream containing a mixture of aromatic hydrocarbons and non-aromatic hydrocarbons; e.g., a naphtha stream, can be sent to a cat naphtha hydrotreater to remove sulfur and nitrogen if their concentrations are substantially greater than 1 ppmw for practical cases. The naphtha hydrotreater or naphtha pretreater uses a conventional hydroprocessing catalyst operating at typical hydrotreater conditions of elevated temperature and pressure in the presence of hydrogen to remove sulfur and nitrogen that can be poisonous to the reforming catalyst. The effluent from the hydrotreater is typically sent to a hydrotreater stabilizer unit which is a distillation tower to remove light gases (H₂, C₁-C₅) from the hydrotreated product. Preferably the feed in the embodiment is a heavy cat naphtha feed and the hydrotreater is a heavy cat naphtha hydrotreater. This hydrotreated naphtha is used as feed stock to membrane separation units wherein the feed is separated into an aromatics-lean/non-aromatics/saturates-rich retentate stream suitable for use as jet fuel or kerosene or a feed to a powerformer, and a permeate stream of increased aromatics hydrocarbon content/decreased non-aromatics/saturated hydrocarbon content for use as gasoline blend stock of increased octane rating.

In another embodiment, naphtha feed, preferably straight run (virgin) naphtha and/or cracked naphtha can be fed to a hydrotreater to be converted into reformer feed. Simultaneously, a feed stream containing a mixture of aromatic hydrocarbons and non-aromatic hydrocarbons, preferably virgin naphtha, thermal cracked naphtha, catalytically cracked naphtha or other streams boiling in the distillate to gasoline boiling range containing aromatic and non-aromatic hydrocarbons, more preferably a hydrocrackate or cracked naphtha stream can be fed to a membrane separation unit wherein an aromatics-lean/non-aromatics-(saturates-)rich retentate and an aromatics-rich/non-aromatics-(saturates-)lean permeate are produced. The permeate is a gasoline blend stock of increased octane rating. The retentate from the membrane separation unit is combined with the reformer feed from the hydrotreater and fed to a reformer for the production of high octane reformer product and co-produced hydrogen.

EXAMPLES Example 1 Increase Hydrogen Production

To demonstrate increased hydrogen production, a simulation of the integrated process was performed using ExxonMobil Research and Engineering Membrane Model and Reformer Model.

The ExxonMobil Research and Engineering Membrane Model is based on the polyester imide copolymer (PEI) membrane as the reference membrane. PEI membranes are described in U.S. Pat. Nos. 4,944,880 and 4,990,275. The membrane model matches well with data collected from lab units and pilot plants while the Reformer Model matches well with data collected from commercial reformer units (CCR or semi-regenerated reformer units).

In the simulation a commercial CCR feed containing 23.1 wt % aromatics was designated as the feed. The properties of CCR feed are listed in Table 1:

TABLE 1 CCR Feed Compositional Profile API Gravity 54.7 Octane, RON 57.8 Composition, wt % Paraffins 43.9 Olefins 0.0 Naphthenes 33.0 Aromatics 23.1 Distillation (D86), ° C. IBP 80 10% 105 30% 113 50% 123 70% 145 90% 164 EBP 181

In the simulated scenario, the feed rate to the CCR unit was set at a constant 52 KBD for both the reference case (no membrane unit) and the present invention case (membrane unit upstream of the CCR unit). The operating conditions are set in the simulation to produce 101 RON (Research Octane Number) reformate. In the inventive scenario employing the membrane separation unit, the unit is simulated to remove 7 KBD permeate from a total of 59 KBD feed to the membrane unit, sending 52 KBD retentate to the reformer from the membrane unit. The membrane unit reduces the aromatics content in the feed to the reformer from 23.1 wt % to 19.3 wt %. Upon running the simulation it was found that by reducing the aromatics content of the feed to the reformer, the net hydrogen production increased by 4.2 MSCFD at the same 52 KBD CCR feed through-put ratio. This is presented in Table 2:

TABLE 2 Performance Comparison for Increased Hydrogen Production Case Reference This Invention Membrane Conditions Membrane SA m2 9539 Feed Flow Rate KBD 59 Feed Temperature ° C. 143 Permeate Vacuum BarA 0.15 Feed Aromatics wt % 23.1 Permeate Product Flow Rate KBD 7 Octane RON 78.8 Aromatics wt % 50 Retentate Product Flow Rate KBD 52 Octane RON 57.8 Aromatics wt % 19 CCR Conditions Flow Rate KBD 52 52 Feed Aromatics wt % 23.1 Retentate 19 Reformate Octane RON 101 101 H₂ Production MSCFD 69.8 73.8

Example 2 Improved Process Efficiency/Energy Conservation

In this simulation only the membrane separation unit is considered because the main goal is to produce a high octane stream for gasoline blending. A commercial hydrocrackate was selected to represent the feed stream in the simulation because it has a relatively high aromatics content. The compositional profile of the hydrocrackate is presented in Table 3:

TABLE 3 Hydrocrackate API Gravity 40.1 Octane, RON 87.3 Composition, wt % Paraffins 7.8 Olefins 0 Naphthenes 31.3 Aromatics 60.9 Distillation (D86), ° C. IBP 97 10% 116 30% 128 50% 139 70% 152 90% 171 EBP 194

As the reference case, hydrocrackate is combined with other CCR feeds and sent directly to the reformer.

In the present invention, the hydrocrackate is first sent to the membrane separation unit where its aromatics content is reduced, the aromatics-rich permeate stream being recovered as high octane gasoline blend stock, and the retentate of reduced aromatics content being sent to the reformer. As shown in Table 4, the permeate produced from the membrane unit would have an RON of 99.1, high enough for use as high octane gasoline blend stock. Based on a feed rate of 6 KBD hydrocrackate to the membrane unit, a permeate was recovered at a rate of 3.33 KBD or 55.5 vol % permeate based on feed. This results in either a net reduction or unloading of 3.33 KBD feed to the reformer based on a combined reformer feed-hydrocrackate feed volume or permits an increase in the feed volume to the reformer reflecting the volume of permeate recovered from the membrane unit, an increase in overall process efficiency and gasoline production capacity.

TABLE 4 Separate hydrocrackate by membrane to improve reformer complex efficiency Membrane Conditions Membrane SA m2 2015 Feed Flow Rate KBD 6 Feed Temperature ° C. 160 Permeate Vacuum BarA 0.013 Feed Aromatics wt % 60.9 Permeate Product Flow Rate KBD 3.33 Octane RON 99.1 Aromatics wt % 79 Retentate Product Flow Rate KBD 2.67 Octane RON 72.1 Aromatics wt % 37.2 Process Efficiency Improvement Net reformer feed reduction KBD 3.33

REFERENCE IS MADE TO THE FIGURES

In FIG. 1 a fully integrated process is presented. In practice, one or more of the sequences employing membrane separation units can be omitted, provided at least one sequence employing a membrane separation unit is used.

A feed stream containing a mixture of aromatic hydrocarbons and non-aromatic hydrocarbons, identified for the sake of convenience as naphtha feed, is employed as feed stock.

Naphtha feed #1 is fed via line (1) into Membrane Unit #1 (2) in which the feed is separated into an aromatics-rich permeate recovered via line (3) and sent to the gasoline blend stock pool and an aromatics-lean retentate sent via line (4) to reformer unit (5), which produces additional high octane gasoline recovered via line (6), which can be stored as such or combined with the high octane permeate in line (3). A hydrogen stream is recovered via line (7).

Optionally or additionally, naphtha feed (2) is fed via line (8) into a FCC naphtha desulfurization process unit (9) with the processed product stream being sent via line (1) to membrane process unit #2 (11) from which a permeate stream rich in aromatics, i.e. a high octane gasoline blend stream is recovered via line (13) and sent to storage or combined with the permeate stream from membrane unit #1 (2) in line (3) and sent to storage.

A retentate stream is recovered from membrane unit #2 (11) and sent via line (12) to the reformer (5) directly or is sent for mixing in line (4) with the retentate from membrane unit #1 (2) and sent as a combined stream to reformer (5).

Optionally or additionally, naphtha feed #3 (preferably heavy cat naphtha) is fed via line (14) to hydrotreater process unit (15) (preferably a heavy cat naphtha hydrotreater process unit). The hydrotreated naphtha from process unit (15) is recovered via line (16) and sent to membrane process unit #3 (17) from which a retentate is recovered via line (18) as jet fuel or kerosene and a permeate of high octane gasoline is recovered via line (19) for storage or moved for mixing with either or both of the permeates from membrane process unit #1 (2) and membrane process unit #2 (11) in lines (3) and (13), respectively.

Make-up feed can be fed via line (4 a) into line (4) for treatment in reformer (5). Make-up feed can be either straight run naphtha or cat or thermally cracked naphtha sent directly to the reformer as it can be straight run naphtha or thermal or cat cracked naphtha which has been hydrotreated prior to being fed via line (4 a) into line (4) and thence under reformer (5).

By practicing the scenario employing membrane process unit #1 (2), the membrane separation performed in the reformer feed (naphtha feed #1) results in a bypass of the aromatics fraction recovered via line (3) around the reformer and opens up the capacity of the reformer to run on higher paraffin content naphthas.

Operation in the scenario employing membrane process unit #2 (11) employs membrane separation on the product recovered from a naphtha desulfurization unit to concentrate aromatics and increase octane rating/quality. The retentate from the membrane unit is sent as primary feed or incremental feed to the reformer. When integrated with the scenario using membrane process unit #1 (2), the permeate yield from membrane process unit #1 can be controlled to produce a retentate volume adjusted to accommodate the retentate volume from membrane unit #2 (11).

Operation in the scenario employing membrane process unit #3 (17) employs the membrane process unit operating on hydrotreated heavy cat naphtha to concentrate aromatics in the permeate and increase octane rating/quality. The retentate is sent to jet or diesel. The octane quality of the permeate from the membrane process unit can be adjusted to allow higher volumes of permeate to be removed from membrane unit #1 (2) when integrated with that unit.

Thus, by combining permeates from membrane unit #1 and membrane unit #3, a target octane can be achieved for the blend while also balancing the hydraulic rates needed to accommodate the retentate from membrane unit #2 being sent to the reformer, thus permitting optimal operation of the reformer while simultaneously producing additional quantities of high octane gasoline blending stock, and hydrogen. 

1. A method for producing gasoline or gasoline blending stock of increased octane rating while also producing a hydrogen stream with increased hydrogen yield comprising contacting a feed stream containing a mixture of aromatic hydrocarbons and non-aromatic hydrocarbons with a membrane in a membrane separation unit wherein the feed is separated into an aromatics-rich/saturates-lean permeate which is a gasoline or gasoline blending stock of increased octane rating and a retentate stream of reduced aromatics content/increased non-aromatics content which is used as feed stream to a reformer wherein the retentate stream is converted in the reformer into high octane reformer gasoline and a gaseous stream of co-produced hydrogen.
 2. The method of claim 1 wherein the feed to the membrane separation unit is selected from virgin naphtha stream, thermal cracked naphtha stream, catalytically cracked naphtha stream, a stream boiling in the distillate to gasoline boiling range containing aromatic and non-aromatic hydrocarbons, or mixtures thereof.
 3. The method of claim 2 wherein the stream is virgin naphtha, thermal cracked naphtha, catalytically cracked naphtha or mixtures thereof.
 4. The method of claim 1 wherein the reformer unit is a continuous catalytic reformer or a semi-regenerated reformer.
 5. The method of claim 4 wherein the stream sent to the reformer comprises the retentate stream from the membrane separation unit combined with other saturates-rich/aromatics-lean refinery streams typically used as reformer feed streams.
 6. The method of claim 4 wherein the retentate sent to the reformer is a combined stream comprising retentate from the membrane separation unit and a retentate from a different membrane separation unit operating on an aromatics/non-aromatics containing feed stream previously subjected to a FCC naphtha desulfurization process.
 7. The method of claim 1 wherein the feed is a naphtha feed previously subjected to hydrotreating in a catalytic naphtha hydrotreater.
 8. The method of claim 1 wherein the feed to the reformer is a combined stream comprising retentate from the membrane separation unit and an effluent stream from a hydrotreater unit which has hydrotreated a feed comprising naphtha.
 9. The method of claim 8 wherein the retentate from the membrane separation unit is retentate recovered from the unit operating on a feed comprising hydrocrackate, cracked naphtha or mixtures thereof.
 10. The method of claim 8 wherein the naphtha feed to the hydrotreater is virgin naphtha, thermal cracked naphtha, catalytically cracked naphtha, a naphtha produced from a hydroprocessing unit, or mixtures thereof.
 11. The method of claim 1, further comprising: providing a second feed stream corresponding to a heavy catalytic naphtha feedstream; hydrotreating the heavy catalytic naphtha under effective hydrotreating conditions; contacting the hydrotreated heavy catalytic naphtha with a membrane to concentrate aromatics in the permeate and increase octane rating/quality while producing a retentate suitable for use as a diesel fuel or a jet fuel. 